Generally, broadcasting services are provided to all users with terminals. Theses broadcasting services are classified into an audio broadcasting service such as radio broadcasting service for providing only audio, a video-centered broadcasting service such as television for providing audio and video services, and a multimedia broadcasting service including audio, video, and data services. The broadcasting services are based on an analog system and are currently evolving into digital broadcasting with the rapid development of various technologies.
Moreover, the broadcasting services are being developed in various systems such as a multimedia service system of a wired network for providing data of high image quality at high rates by wire, a system for providing a multimedia service using an artificial satellite, and a system that simultaneously uses a wire and an artificial satellite, without use of a conventional system for providing a service on the basis of a transmission tower.
A Digital Multimedia Broadcasting (DMB) system, as one of the above-described systems, is being actively commercialized. This DMB system has been derived from Digital Audio Broadcasting (DAB) and is based on European Research Coordination Agency (Eureka) project-147, serving as the technical standard of DAB in Europe.
In Europe, as the origin of the DAB technology, a group called Digital Video Broadcasting (DVB) has been organized for multimedia broadcasting services and is working to establish a separate standard for portable broadcasting services, called Digital Video Broadcasting-Handhelds (DVB-H). DVB-H is a new broadcasting standard under development by Digital Audio Broadcasting (DAB) that is a European group for digital TV broadcasting standardization, following satellite digital TV (DVB-S), digital cable TV (DVB-C), and terrestrial digital TV (DVB-T).
With the determination that voluminous multimedia contents such as movies or broadcast dramas cannot be implemented through portable terminals in accordance with 3rd mobile communication (Universal Mobile Telecommunication System (UMTS) or International Mobile Telecommunications-2000 (IMT-2000)), terrestrial digital TV, and DAB, the DAB group has promoted standardization named ‘DVB-eXtension (DVB-X)’, which was later renamed DVB-H to clearly indicate ‘portable broadcasting’.
DVB-H is designed to reinforce mobility in the European digital TV transmission standard DVB-T and is an extension of DVB-T considering low power, mobility, and portability of mobile terminals or portable video devices. DVB-H systems support additional Error Correction Coding (ECC) for layer-3 Internet Protocol (IP) packets. This additional ECC process is called Multi Protocol Encapsulation—Forward Error Correction (MPE-FEC).
In DVB-H systems, broadcasting data is composed of IP datagrams and an MPE-FEC frame is formed by performing Reed-Solomon (RS) coding on the IP datagram. Thus, the MPE-FEC frame is composed of an MPE section carrying the IP datagram and an MPE-FEC section carrying parity data resulting from the RS encoding. The MPE section and the MPE-FEC section are transmitted through a payload of a TransportStream (TS) packet, which is a transport unit of the DVB-H system, over a physical layer.
FIG. 1 illustrates a data structure of a TS packet in a general DVB-H system.
FIG. 1(A) illustrates a TS packet for storing an MPE section or MPE-FEC section. The TS packet (a) may include a plurality of MPE sections or MPE-FEC sections or a single MPE section or MPE-FEC section may be transmitted through a plurality of TS packets. If a Packet Identifier (PAD) of a header 101 of the TS packet (a) indicates a packet transmitting an MPE section or MPE-FEC section, a receiving side considers an MPE section or MPE-FEC section (b) as being received through a payload 103. If the PID of the header 101 does not indicate the packet transmitting the MPE section or MPE-FEC section, it can be appreciated that Program Specific Information/Service Information (PSI/SI) is included in the payload 103.
FIG. 1(B) is a diagram illustrating an MPE section carrying an IP datagram or an MPE-FEC section carrying parity data of IP datagrams. The MPE or MPE-FEC section is composed of a header 105 and a payload 107. The header 105 includes information representing whether data contained in the payload 107 is an MPE section or MPE-FEC section. The payload 107 stores the IP datagram (c) or parity data of the IP datagram (c).
FIG. 1(C) is a diagram illustrating an IP datagram. The IP datagram represents a packet including a header 109 storing address information of an end for transmitting data and a payload 111 carrying broadcast data.
FIG. 2 is a diagram for explaining RS encoding performed by a transmitter of a general DVB-H system. The DVB-H transmitter generally performs a single RS encoding operation in each of a physical layer and a link layer. RS encoding explained in FIG. 2 is performed in the link layer.
Referring to FIG. 2, in the DVB-H system, an MPE-FEC frame can be represented by a horizontal-direction (i.e., column) size 200 and a vertical-direction (i.e., row) size 202. The column 200 is composed of 255 bytes, in which a left region of 191 bytes is an application data cable region 204 for storing an MPE section including an IP datagram 100 that is broadcast data and a right region of 64 bytes is an RS data table region 206 for storing RS data or parity data resulting from RS encoding with respect to broadcasting data stored in the application data table region 204. In contrast, the row 202 is variable up to 1024 rows.
As illustrated in FIG. 2, IP datagrams 100 of ‘N’ number are stored in the application data table region 204 along the vertical direction. If the application data table region 204 is not filled with the first through Nth IP datagrams, the application data table region 204 is entirely filled up by filling up the remaining space with zero, i.e., performing zero padding 208 on the remaining space.
Once the application data table region 204 is entirely filled with the IP datagrams or zero as a result of the zero padding, RS encoding is performed in the horizontal direction, and parity data resulting from the RS encoding is filled in an RS data table region 206 as illustrated in FIG. 2.
FIG. 3 is a diagram for explaining timing slicing for transmission of a TS packet in a transmitter of a general DVB-H system. A general transmitter generally transmits data with a fixed bandwidth 306, but a transmitter of a DVB-H system transmits a burst of predetermined data as in burst size 310. The DVB-H system supports time slicing to reduce power consumption of a receiver. Time slicing means data transmission in bursts. In other words, data to be transmitted during the entire time duration 300 is transmitted only during a burst duration 302 by increasing a data rate. Thus, the entire time duration 300 can be divided into the burst duration 302 during which data transmission occurs and an off-time duration 304 during which no data transmission occurs.
In FIG. 3, the fixed bandwidth 306 indicates an average bandwidth for general stream transmission without time slicing, and the burst bandwidth 308 indicates a burst bandwidth for transmission of the transmitter in the DVB-H system. The entire time duration 300 lasts from the start of current burst transmission until the start of next burst transmission, and is divided into the burst duration 302 during which data transmission occurs and the off-time duration 304 during which no data transmission occurs. The burst duration 302 indicates the start and end intervals of burst transmission, and the off-time duration 304 during which any transport packet is not transmitted exists between burst durations. A single MPE-FEC frame can be transmitted per burst size 310.
In the DVB-H system, a receiver receiving an MPE-FEC frame as above frequency-down converts a received broadcast signal and converts the broadcast signal into a digital signal of an OFDM symbol form. Then, the receiver restores OFDM symbols to an original TS packet. In the receiver, a time slicing processor performs a switching operation to receive a TS packet included in an MPE-FEC frame per predetermined burst duration. The receiver can identify the burst duration through delta_T information that indicates the start of a next burst duration included in a header of each MPE section and MPE-FEC section.
FIG. 4 is a timing diagram illustrating a process of processing time slicing and MPE-FEC in a receiver of a general DVB-H system.
Referring to FIG. 4, an RF demodulator turns on at a time earlier by a warmup time of the RF demodulator from a time designated by delta_T. Next, burst data is received and a section is detected, thus constituting an MPE-FEC frame. An MPE section to be stored in an application data region and an MPE-FEC section to be stored in an RS data region are transmitted with a temporal sequence. The last section has a frame border information value of ‘1’ and, immediately after this section is detected, a time slicing controller commands ‘OFF’ to the RF demodulator and a DVB-H physical layer demodulator, and an MPE-FEC processor initiates an MPE-FEC decoding operation. Due to the influence of fading and the like, an error takes place in burst data and thus, the last section may not be detected. In this case, the RF demodulator and the DVB-H physical layer demodulator are continuously operated to wait the last section, thus causing a problem that the receiver operates continuously with the maximum power.
A solution to the above problem is the use of a settable Maximum Burst Duration (MBD). That is, if a preset MBD lapses after a start time of a current burst (after calculation with a previous delta_T), the time slicing controller compulsorily determines that it is a burst end time, and commands ‘OFF’ to the RF demodulator and the DVB-H physical layer demodulator, but the above method also has a problem of causing power consumption during an MBD.